Capturing the Upper Colorado River

About 16 million years ago, the basin-and-range country of far western Arizona formed, causing drainage to increase from the rising plateaus in the Grand Canyon region. The increasing drainage filled the basins between the mountains, creating lakes that eventually overflowed, breaching the rim of the basin, and creating a lake in the next lower basin. A succession of these events created the modern course of the Colorado River along the borders of Arizona, Nevada, and California, downstream from the Grand Canyon. The increasing runoff also caused the ancestral lower Colorado River to erode headward to the east, ultimately capturing the drainages of older canyons. The portion of the Grand Canyon between Parashant Canyon and Peach Spring Wash has been dated at 70 million years, much older than the far western or eastern portions of the Canyon. This section appears to have been part of an ancient canyon system that drained to the north, into Utah. When the lower Colorado River captured this canyon, it reversed the flow and added its run off to its own. This process was probably repeated many times, and eventually, the headward-eroding lower Colorado River captured the ancestral upper Colorado River and the Little Colorado in the vicinity of the present confluence of the Little Colorado and Colorado rivers.

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